A “machine room fire” alarm was tripped at 8 am on a telephone maintenance line in a plant producing meat or fish-based foods. Smoke exited from the extraction shaft. The installations were shut down as an emergency response. Fire broke out on the compressor motor of a refrigeration unit containing 2.45 tonnes of ammonia (NH3). The refrigerant leaked; 4 employees wearing self-breathing apparatuses, including 2 maintenance technicians, tried to control the fire source using extinguishers. In order to limit NH3 emissions, the response team closed 2 manual shutoff valves on the NH3 collector pipes in addition to the automatic valves. External fire-fighters and the subcontractor responsible for maintaining the installations were notified. The facility’s general fire alarm was activated, and the plant’s 116 employees made their way to designated shelters.

At 8:30 am, major rescue operations were being deployed, including: 41 fire-fighters, a chemical emergency squad, veterinary agencies, and gendarme officers. The fire was extinguished shortly thereafter. At 9:30, 2 fire-fighters wearing diving suits set out to identify the source of the leak. A non-localised, high-pitched whistling sound disturbed their efforts and persisted until closing a compressed air valve, which served to isolate the plant at 9:45. Wearing a self-breathing suit and protected by fire-fighter escort, a pair of technicians with the subcontracted maintenance firm entered the premises at 9:50 am. The NH3 leak was brought under control at 10:24 on a loose-fitting rigid pipe connection whose joint had been deteriorated by flames. Extraction ventilation remained turned on until the emergency intervention inside the premises and attic area had been completed; 4 ppm of NH3 were measured 100 m from the site.

This emergency intervention was concluded around 11:30 am. No confined NH3 explosion was observed and no injuries reported. Only the compressor and piping involved in the accident were damaged. Since the premises were separated from the production equipment and a 2nd compressor was available, the plant was able to resume activity around 11 that morning. A 150-kg additional supply of NH3 was delivered upon start-up of the 2nd compressor; this quantity however was definitely not the only substance lost during the accident.

According to the operator, a series of frictions and vibrations on an electrical terminal block of the motor-compressor loosened lug nuts, causing an electrical blast that sparked the fire. Several measures were adopted, namely: disposal of oil cans stored onsite, identification of manual dam valves, repositioning of an air valve located in the attic, rapid cleaning of the premises (soot removal, etc.) in order to limit equipment corrosion, revision of the internal emergency plan, distribution of personnel information and training (background material, NH3 risk, use of self-breathing apparatus during a service call). Quickly detected, localised and then treated, this accident could have been much more serious during a slower period of activity (e.g. weekend, night shift). The investigation revealed that the plant’s maintenance manager was not adequately familiar with the refrigeration installations, whose maintenance had been subcontracted to an outside firm.